Two lines build the same board with the same components. One has a documented electrostatic control programme with daily verification of straps, footwear and benches; the other has the mats and the straps, and nobody checks whether they work. Both look identical from the doorway, and their field failure rates do not.
ESD control on a charger line: what the programme covers
An electrostatic control programme covers the protected area, personnel grounding, work surfaces and flooring, handling rules, and verification records.
The purpose is to keep charge from accumulating on people and surfaces, and to discharge what does accumulate in a controlled way rather than through a semiconductor junction. Damage is often latent: a device that passes the functional test and fails in the field after a few thermal cycles.
The programme is judged by its records rather than by its equipment list, because every element of it can be present and unverified. That is where a buyer’s audit produces the most information, and it takes minutes rather than days.
The protected area and what defines it
The defined area is where the controls apply, and its boundary is marked.
Inside it, benches are dissipative, flooring is dissipative or the operator is grounded by other means, and the movement of charged material in and out is controlled. The practical questions are whether the boundary is marked and physically respected, and whether the entrance has a means of testing the person before they start work. Where the boundary exists only on a drawing, the controls apply nowhere in particular.
Personnel grounding: wrist straps, footwear and testing
The control only exists if it is verified daily.
Wrist straps are tested at the start of each shift with a documented result, and where footwear and flooring are the grounding method, the combination is tested as a system rather than assumed. Confirm it by asking for the log from the previous day, and by asking what happens when a strap fails the test. The answer to the second question is the difference between a control and a ritual.
Work surfaces, flooring and ionisation
Three elements, and they interact.
Bench surfaces are dissipative and connected to a common ground point; flooring is dissipative where the operator’s grounding depends on it; and ionisers are used where insulating materials cannot be removed and charge accumulates anyway. The resistance measurements for surfaces and flooring are recorded at defined intervals, and the ionisers are verified as part of the same programme rather than treated as an installation.
Handling rules for boards, coils and finished assemblies
Most damage happens in handling rather than at the station.
Boards travel in shielded packaging; components are removed from their packaging only inside the protected area; finished assemblies are handled by their enclosures where possible; and anything leaving the area goes into packaging that protects it. Confirm it by following a board from incoming to assembly and watching where it is touched and where it is stored in between.
| Element | Requirement | Verification | Common failure |
|---|---|---|---|
| Protected area | Defined and marked boundary | Inspection of the boundary and entry test | Described but not marked |
| Personnel grounding | Wrist strap or footwear system | Daily test log with results | Straps worn, never tested |
| Surfaces and flooring | Dissipative, connected to ground | Periodic resistance measurements | Measured once at installation |
| Ionisation | Where insulating material is unavoidable | Periodic verification of the units | Treated as an installation |
| Handling | Shielded packaging and defined touch points | Observation of the route | Storage outside the area |
Packaging and transport of sensitive parts
The control follows the component, not the room.
Semiconductors arrive in packaging that protects them and stay in it until they are inside the protected area; boards travel between stations in shielded totes; and any part returned for rework goes back into protective packaging rather than into a bag. Confirm it by asking how a board travels from the surface-mount line to hand assembly, and whether the same totes come back into the area from the packing end.
What a buyer should ask for
Four documents, and each is short.
The programme description with the boundary of the protected area; the daily verification log for personnel grounding; the periodic measurement records for surfaces, flooring and ionisers; and the handling instruction covering the route from incoming to packing. Where a factory cannot produce the daily log, the other three describe intentions, and the failure mode that follows is latent damage that appears months later as a field return with no obvious cause.
FAQ
How do we tell whether ESD damage is the cause of a field failure?
Latent damage usually appears as a parameter that drifts or a failure that appears after thermal cycling, without a visible defect. The evidence is the comparison between units built under controlled conditions and those that were not, plus the verification records from the line. Compare units built under controlled conditions with those that were not, and read the line’s verification records alongside the comparison.
Is a wrist strap necessary if the floor is dissipative?
One reliable path to ground is enough, provided it is verified. Where footwear and flooring provide it, the combination is tested as a system; where a wrist strap is used, it is tested daily. Assuming both without testing either is the failure mode. Where footwear and flooring provide the path it is tested as a system, and where a wrist strap is used it is tested daily, because assuming both without testing either is the failure mode.
Does a charger assembly really need this?
The control applies from the point where semiconductors and boards are exposed. A product that is assembled from sealed sub-assemblies has a narrower exposure than one where boards are handled and programmed in house, and the programme should be scoped accordingly. Scope it from the point where semiconductors and boards are exposed, because a product assembled from sealed sub-assemblies has a narrower exposure than one programmed in house.
What is the most common gap found in an audit?
The daily personnel test log, followed by storage of boards outside the protected area. Both are inexpensive to correct and both are invisible without the records, which is why they persist. The daily personnel test log comes first, followed by storage of boards outside the protected area, because both are inexpensive to correct and both are invisible without the records, which is why they persist.
Next step
Send the board handling route, the assembly steps and the market requirements to Wecent Group through the contact page. The reply describes the protected area for the product, the verification records kept and how handling is controlled between stations. Related reading: the factory floor, OEM and ODM charger manufacturing and charger manufacturing services. External references: ESD Association standards, ESD Association, IEC standards, IEC Webstore, UL standards and certification and TUV testing services.
{“@context”:”https://schema.org”,”@type”:”FAQPage”,”mainEntity”:[{“@type”:”Question”,”name”:”How do we tell whether ESD damage is the cause of a field failure?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”Latent damage usually appears as a parameter that drifts or a failure that appears after thermal cycling, without a visible defect. The evidence is the comparison between units built under controlled conditions and those that were not, plus the verification records from the line.”}},{“@type”:”Question”,”name”:”Is a wrist strap necessary if the floor is dissipative?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”One reliable path to ground is enough, provided it is verified. Where footwear and flooring provide it, the combination is tested as a system; where a wrist strap is used, it is tested daily. Assuming both without testing either is the failure mode.”}},{“@type”:”Question”,”name”:”Does a charger assembly really need this?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”The control applies from the point where semiconductors and boards are exposed. A product that is assembled from sealed sub-assemblies has a narrower exposure than one where boards are handled and programmed in house, and the programme should be scoped accordingly.”}},{“@type”:”Question”,”name”:”What is the most common gap found in an audit?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”The daily personnel test log, followed by storage of boards outside the protected area. Both are inexpensive to correct and both are invisible without the records, which is why they persist.”}}]}